The present invention relates, in general, to sensing and controlling the temperature of multi-panel heated assemblies and, in particular, to a thermal probe for sensing the temperature of one panel of an optically transparent, multi-panel assembly which has a radiant heater and by which radiation losses, such as those by an infant in an infant incubator, are reduced.
Infant incubators are used in the treatment and maintenance of weak, sickly, premature or low birth weight infants in order to maintain infant body temperature and allow the infant to develop. Infants may lose heat in four ways: through evaporation, convection, conduction and radiation. Conductive heat loss in an infant is usually considered negligible, since the mattress upon which the infant is placed is generally an excellent insulator and, therefore, such net heat loss is small. Evaporative heat loss is dependent upon the incubator air temperature and infant skin temperature differential, as well as the relative humidity of the incubator air and the air velocity across the infant's skin. Evaporative heat loss is often referred to as insensible water loss and can be controlled by controlling the air flow characteristics of the incubator design, the incubator air temperature, and by adding humidity to the incubator air. Convective heat loss is also a function of the incubator air temperature and infant skin temperature differential. Radiative or radiant heat loss is a function of infant skin temperature and incubator wall temperature differential. Radiant heat loss is typically the major source of heat loss, except in the very first days in the life of a very premature, very low birth weight infant, when evaporative heat loss (insensible water loss) may be greater.
The amount of heat loss by any of the ways mentioned is dependent upon incubator design and the metabolism of the infant. The desired objective of an incubator environmental control system is to provide a thermal environment which will place minimum demand on the metabolism of the infant to maintain body temperature at the preferred level. Typically, this state of minimum metabolic demand is assumed to be achieved when the skin temperature of an infant is maintained within a prescribed normal range.
Radiant heat loss from the infant may be reduced by minimizing radiant heat loss through the walls of the incubator. This is because the primary source of radiant heat loss in an incubator is cold incubator walls. One approach for minimizing radiant heat loss is to increase the wall temperature of the incubator, thereby minimizing the temperature differential between the infant and the incubator walls.
In U.S. Pat. No. 5,119,467 and entitled TRANSPARENT FILM RADIANT HEAT SOURCE FOR USE WITH INCUBATORS and in copending application Ser. No. 847,926 filed concurrently herewith and also entitled TRANSPARENT FILM RADIANT HEAT SOURCE FOR USE WITH INCUBATORS, both assigned to the same assignee as the assignee of this application, a transparent radiant film is applied to one panel of a multi-panel assembly, either in the form of an incubator hood or an overlay for an incubator hood. The radiant film, when powered, raises the temperature of the incubator hood, thereby reducing radiant heat losses, and also can provide radiant heat which affects the air temperature within the incubator hood.
In using such radiant heaters, it is important to accurately control the temperature of the incubator walls. This, in turn, requires proper and accurate sensing of the wall temperature of the incubator hood.